The clutch cover assembly of the foregoing type has been described in Published Utility Model Application No. 58-157030 applied for patent by the applicant of this invention. In that structure, a large-size main diaphragm spring (abbreviated merely to a diaphragm spring hereinunder) connected to a pressure plate and a sub diaphragm spring (abbreviated merely to a coned disc spring hereinunder) are installed in a diaphragm spring mechanism.
A general diaphragm spring has a characteristic that a deflection load increases when a deflection amount decreases from some value to a specified value and the deflection load decreases when the deflection amount decreases further.
For this reason, in a general structure in which only the diaphragm spring is used as the diaphragm spring mechanism, when the friction facing is worn out, a deflection load of the diaphragm spring increases with a decrease in a deflection amount of the diaphragm spring at the time of clutch engagement. As the result, an urging force effected from the diaphragm spring on a pressure plate increases so that a required treading force of a clutch pedal increases too.
On the contrary, in the structure of the foregoing application, the deflection load of the coned disc spring varies so as to counteract the increase in the load of diaphragm spring. As the result, the urging force effected from the diaphragm spring on the pressure plate is maintained at approximately a constant value so that the required treading force of the clutch pedal is also maintained at an approximately constant value.
However, the coned disc spring is not locked in its rotating direction in the structure of the foregoing application, so that the coned disc spring would rotate in relation to other members to cause an emission of abnormal sound under a state where the deflection load is not applied on the coned disc spring, i.e. under a clutch disengaged state. Further, since the coned disc spring is not supported in its axial direction, some axial play would be produced so that the coned disc spring would vibrate in its axial direction to cause the emission of abnormal sound.